Exam 3 Biology - Chapter 14 Planned breeding...

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Chapter 14 Planned breeding experiments-organisms are bred and results are analyzed Planned breeding experiments show variation in characteristics, produce large number of offspring, allows for controlled mating, usually have short life cycles, and is convenient to handle Pedigree analysis-examines history of inheritance of traits and is used for when controlled matings cannot be done Modern genetics-mainly due to work of Gregor Mendel who worked in late 1850s Mendel used garden peas, which had true breeding varieties. True breeding is when the plants self-pollinate, the offspring are all of the same variety. He studied the inheritance of seven characteristics that existed in 2 forms. Each variant for a characteristic is called a trait. He tracked heritable characteristics for 3 generations A monohybrid cross tracks the inheritance of a single characteristic. P generation is the parents. F1 generation is the first filial offspring. F2 generation is the second filial offspring. Mendel used true breeding parents, purple and white flowers. The F1 generation all had purple flowers. In F2, 3 had purple, 1 had white. Yellow seeds dominant to green. Purple flowers dominant to white. Round seeds dominant to wrinkled. When gametes are formed, the two alleles separate, so that each gamete only has one. Law of segregation: members of a pair of genes separate from each other during gamete formation. Alternative versions of genes (different alleles) account for variations in inherited characteristics. For each characteristic an organism inherits 2 alleles, one from each parent. If 2 alleles differ, then the dominant allele is fully expressed in the organism’s appearance. The recessive allele has no noticeable effect on the organism’s appearance.
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The 2 alleles for each characteristic segregate during game production. The genotype is the genetic composition of an organism. Phenotype is the outward appearance of an individual. A test cross is done to determine the genotype of a parent with a dominant phenotype. The unknown genotype is crossed with homozygous recessive. Law of Independent Assortment: each pair of alleles segregates independently of each other pair of alleles during gamete formation. This applies only to genes located on different chromosomes. In complete dominance, the phenotypes of the heterozygote and dominant homozygote are indistinguishable. In incomplete dominance, neither allele is completely dominant. The heterozygous phenotype is a blend of the two alleles. When red and white snapdragons are crossed, the heterozygotes are pink. In codominance, the two alleles each affect the phenotype in separate distinguishable ways. In blood type, A and B alleles are codominant. Heterozygotes have AB phenotype. Tay-Sachs disease is recessively inherited.
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